The present invention relates generally to a scissor lift and, more particularly, to a low-profile, scissor lift mechanism utilizing a bell crank mechanism for use on a coil car or the like.
Scissor lift tables are well known for facilitating the stacking or unstacking of articles on pallets or other supports. The typical lift table incorporates a support platform and a mechanism for selectively raising or lowering the support platform into a position facilitating its loading or unloading. Vertical movement of the support platform usually is accomplished via a scissor arm mechanism that supports the support platform on an underlying base and that is raised and lowered by way of one or more hydraulic or pneumatic cylinders.
On traditional single scissor arm lift mechanisms, the hydraulic cylinder or linear actuator is typically mounted on one scissor arm or the base of the lift and attached to another scissor arm on opposite sides of a scissor pivot point. One problem with these types of mechanisms having generally vertically positioned cylinders is that they typically have a high profile. Low profile, cam style scissor lift mechanisms have been developed in which the hydraulic cylinder is mounted generally horizontally to a lift frame on one side and to a crossmember on the other side. The crossmember engages opposing legs of the pair of scissor arms below the scissor pivot points utilizing needle bearing cam follower leg rollers at either end of the crossmember. The actuation of the hydraulic cylinder forces the crossmember to move along an incline such that, as the hydraulic cylinders extend further, the crossmember is raised vertically and moved horizontally which causes the scissor legs to extend and lift the platform vertically.
However, traditional low profile lift mechanisms still have several problems. The strength of prior art low profile, cam style lift mechanisms is significantly lower in that they typically have a capacity rated below 30,000 pounds. Uneven loads produce significant torsional loads on the scissor legs and other support members of prior art low profile lift mechanisms. In addition, the friction and eccentric loading between the sliding/rolling members add work and produce wear on the mechanisms and the hydraulic cylinder. Another problem with the prior art lifts is that the mechanisms deflect significantly under load and have large differences in strength ratings between the retracted and the extended positions.
These and other problems in the prior art reveal the need for a new lift mechanism which overcomes one or more of the above-mentioned problems.
It is an object of the invention to provide an improved lift mechanism utilizing a bell crank style crank arm assembly for use with a low profile scissor lift which overcomes one or more of the problems identified with the prior art. These and other advantages are provided by a scissor lift comprising: a frame; a deck moveable relative to the frame between an extended and a retracted position; a first leg supporting the deck on the frame having a first end pivotally attached to the frame, a second end slidably and pivotally attached to the deck, and an intermediate portion therebetween; a second leg supporting the deck on the frame having a first end slidably and pivotally attached to the frame, a second end pivotally attached to the deck, and an intermediate portion therebetween; wherein the second leg is transverse to the first leg and wherein the intermediate portions of the first leg and the second leg are pivotally connected about a first shaft; and a means for applying a generally vertical force to the first shaft to move the deck between a retracted position and an extended position.